Image file formats provide a standardized method of organizing and storing image data.
This article deals with digital image formats used to store photographic and other image information. For disk image file formats see Disk image. A disk image is a single File containing the complete contents and structure representing a data storage medium or device such as a Hard drive, CD, or
Image files are made up of either pixel or vector (geometric) data, which is rasterized to pixels in the display process, with a few exceptions in vector graphic display. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position In Computer graphics, a raster graphics image or bitmap, is a Data structure representing a generally rectangular grid of Pixels Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based The pixels that make up an image are in the form of a grid of columns and rows. Each pixel in an image consists of numbers representing brightness and color.
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Image file sizes
Image file sizes, expressed in bytes, increase with the number of pixels in the image, and the color depth of the pixels. A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. The more rows and columns, the greater the image resolution and the greater the file size. Image resolution describes the detail an Image holds The term applies equally to Digital images film images and other types of images Also, each pixel making up the image increases in size as color depth is increased. An 8-bit pixel (1 byte) can store 256 colors and a 24-bit pixel (3 bytes) can store 16 million colors. The latter is known as truecolor. See also True Colors (disambiguation. Truecolor is a method of representing and storing graphical image information (especially in computer
Image compression is a method of using algorithms to decrease file size. In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation High resolution cameras produce large image files. Files sizes may range from hundreds of kilobytes to many megabytes depending on the resolution of the camera and the format used to save the images. High resolution digital cameras record 8 megapixels (MP) (1MP= 1000000 pixels/ 1 million) images, or more, in truecolor. Many compact digital still cameras can record Sound and moving Video as well as still Photograph. Consider an image taken by an 8 MP camera. Since each of the pixels uses 3 bytes to record true color, the uncompressed image would occupy 24,000,000 bytes of memory. That is a lot of storage space for just one image, and cameras must store many images to be practical. Faced with large file sizes, both within the camera, and later on disc, image file formats have been developed to address the storage problem. An overview of the major graphic file formats is given below.
Image file compression
There are two types of image file compression algorithms: lossy and lossless. A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original but is close enough to be useful Lossless data compression is a class of Data compression Algorithms that allows the exact original data to be reconstructed from the compressed data
Lossless compression
Lossless compression algorithms reduce file size with no loss in image quality, though they usually do not compress to as small a file as a lossy method does. When image quality is valued above file size, lossless algorithms are typically chosen.
Lossy compression
Lossy compression algorithms take advantage of the inherent limitations of the human eye and discard information that cannot be seen. Most lossy compression algorithms allow for variable levels of quality (compression) and as these levels are increased, file size is reduced. At the highest compression levels, image deterioration becomes noticeable. This deterioration is known as compression artifacting.
The images linked below demonstrate the noticeable artifacting associated with lossy compression algorithms. Click on the thumbnail image to view the full size version.
NOTE: The two images above are designed to be illustrative only. Both were converted from a losslessly compressed RAW image in Adobe Photoshop CS2. The "lossy" image was repeatedly opened and resaved using a low JPEG quality setting to increase visual artifacting and then exported as a PNG, while the "lossless" image was saved once as a PNG to minimize visual artifacting.
Exif
The Exif (Exchangeable image file) format is an algorithm incorporated in the JPEG software used in most cameras. Exchangeable image file format ( Exif) is a specification for the Image File format used by Digital cameras The specification uses the existing Exchangeable image file format ( Exif) is a specification for the Image File format used by Digital cameras The specification uses the existing Its purpose is to record and to standardize the exchange of data between digital cameras and editing and viewing software. The data are recorded for individual images and includes such things as: camera settings, time and date, shutter speed, exposure, image size, compression, name of camera, color information, etc. When images are viewed or edited by image editors, such as Paint Shop Pro, all of this image information can be displayed.
Major graphic file formats
There are many graphic file formats, if we include the proprietary types. The PNG, JPEG, and GIF formats are most often used to display images on the Internet. These graphic formats are listed and briefly described below, separated into the two main families of graphics: raster and vector.
Raster formats
These formats store images as bitmaps (also known as pixmaps). In Computer graphics, a bitmap or pixmap is a type of memory organization or Image file format used to store Digital images The For a description of the technology aside from the format, see Raster graphics. In Computer graphics, a raster graphics image or bitmap, is a Data structure representing a generally rectangular grid of Pixels
JPEG
JPEG (Joint Photographic Experts Group) files are a lossy format (in most cases). The DOS filename extension is JPG, although other operating systems may use JPEG. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Nearly all digital cameras have the option to save images in JPEG format. The JPEG format supports 8 bits per color – red, green, and blue, for 24-bit total – and produces relatively small file sizes. The compression when not too severe does not detract noticeably from the image. But JPEG files can suffer generational degradation when repeatedly edited and saved. Photographic images may be better stored in a lossless non-JPEG format if they will be re-edited in future, or if the presence of small "artifacts" (blemishes), due to the nature of the JPEG compression algorithm, is unacceptable. JPEG is also used as the image compression algorithm in many Adobe PDF files.
TIFF
TIFF (Tagged Image File Format) is a flexible image format that normally saves 8 or 16 bits per color – red, green and blue – for a total of 24 or 48 bits, and uses a filename extension of TIFF or TIF. TIFF's flexibility is both a feature and a curse, with no single reader capable of handling all the different varieties of TIFF files. TIFF can be lossy or lossless. Some types of TIFF files offer relatively good lossless compression for bi-level (black and white, no grey) images. A binary image is a Digital image that has only two possible values for each Pixel. Some high-end digital cameras have the option to save images in the TIFF format, using the LZW compression algorithm for lossless storage. Lempel-Ziv-Welch ( LZW) is a universal Lossless data compression Algorithm created by Abraham Lempel, Jacob Ziv, and Terry The TIFF image format is not widely supported by web browsers. TIFF is still widely accepted as a photograph file standard in the printing industry. TIFF is capable of handling device-specific color spaces, such as the CMYK defined by a particular set of printing press inks.
RAW
RAW refers to a family of raw image formats that are options available on some digital cameras. A raw image file contains minimally processed data from the image sensor of a Digital camera or Image scanner. These formats usually use a lossless or nearly-lossless compression, and produce file sizes much smaller than the TIFF formats of full-size processed images from the same cameras. The raw formats are not standardized or documented, and differ among camera manufacturers. Many graphic programs and image editors may not accept some or all of them, and some older ones have been effectively orphaned already. Adobe's Digital Negative specification is an attempt at standardizing a raw image format to be used by cameras, or for archival storage of image data converted from proprietary raw image formats. In Digital photography, the Digital Negative ( DNG) File format is a Royalty free RAW image format designed by Adobe Systems
PNG
The PNG (Portable Network Graphics) file format is regarded, and was made, as the free and open-source successor to the GIF file format. Portable Network Graphics ( PNG) is a bitmapped image format that employs Lossless data compression. The PNG file format supports true color (16 million colors) whereas the GIF file format only allows 256 colors. PNG excels when the image has large areas of uniform color. The lossless PNG format is best suited for editing pictures, and the lossy formats like JPG are best for final distribution of photographic-type images because of smaller file size. Many older browsers do not yet support the PNG file format, however with the release of Internet Explorer 7 all popular modern browsers fully support PNG. The following tables compare general and technical information for a number of Web browsers Please see the individual products' articles for further information The Adam7-interlacing allows an early preview even when only a small percentage of the data of the image has been transmitted. Adam7 is the interlacing Algorithm specified for use in PNG images
GIF
GIF (Graphics Interchange Format) is limited to an 8-bit palette, or 256 colors. This makes the GIF format suitable for storing graphics with relatively few colors such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single color, and ineffective for detailed images or dithered images. Dither is an intentionally applied form of Noise, used to randomize Quantization error, thereby preventing large-scale patterns such as contouring that are more objectionable
BMP
The BMP file format (Windows bitmap) is used internally in the Microsoft Windows operating system to handle graphics images. The BMP file format, sometimes called bitmap or DIB file format (for device-independent bitmap) is an Image file format used to store Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. These files are typically not compressed, resulting in large files. The main advantage of BMP files is their wide acceptance, simplicity, and use in Windows programs.
PPM, PGM, PBM, PNM
Netpbm format is a family including the portable pixmap file format (PPM), the portable graymap file format (PGM) and the portable bitmap file format (PBM). The portable pixmap file format ( PPM) the portable graymap file format ( PGM) and the portable bitmap file format ( PBM) specify rules These are ASCII files that provide very basic functionality and serve as a least-common-denominator for converting pixmap, graymap, or bitmap files between different platforms. American Standard Code for Information Interchange ( ASCII) Several applications refer to them collectively as the PNM format (portable anymap).
Vector formats
- See also: Vector graphics
As opposed to the raster image formats above (where the data describes the characteristics of each individual pixel), vector image formats contain a geometric description which can be rendered smoothly at any desired display size. Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based
Vector file formats can contain bitmap data as well. 3D graphic file formats are technically vector formats with pixel data texture mapping on the surface of a vector virtual object, warped to match the angle of the viewing perspective. 3D computer graphics (in contrast to 2D computer graphics) are graphics that use a three-dimensional representation of geometric data that is stored in the computer Texture mapping is a method for adding detail surface texture or colour to a computer-generated graphic or 3D model.
At some point, all vector graphics must be rasterized in order to be displayed on digital monitors. However, vector images can be displayed with analog CRT technology such as that used in some electronic test equipment, medical monitors, radar displays, laser shows and early video games. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or Electronic test equipment (sometimes called "testgear" is used to create signals and capture responses from electronic Devices Under Test (DUTs A medical monitor is an automated Medical device that senses a patient's Vital signs and displays the results Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships A laser lighting display or laser Light show involves the use of Laser light to entertain an audience Spacewar! is one of the earliest known digital Computer games Steve "Slug" Russell, Martin "Shag" Graetz and Wayne Wiitanen Plotters are printers that use vector data rather than pixel data to draw graphics. A plotter is a Vector graphics printing device that connects to a Computer.
SVG
SVG (Scalable Vector Graphics) is an open standard created and developed by the World Wide Web Consortium to address the need (and attempts of several corporations) for a versatile, scriptable and all-purpose vector format for the web and otherwise. An open standard is a Standard that is publicly available and has various rights to use associated with it The term DOM Scripting refers to programmatically accessing the Document Object Model (DOM The SVG format does not have a compression scheme of its own, but due to the textual nature of XML, an SVG graphic can be compressed using a program such as gzip. Don't change "Extensible" gzip is a Software application used for File compression. gzip is short for GNU zip; the program is a Free software replacement for the Because of its scripting potential, SVG is a key component in web applications: interactive web pages that look and act like applications. In Software engineering, a web application or webapp is an application that is accessed via Web browser over a network such as the Internet
Others
Other image file formats of vector type include:
See also
External links
- Description of Bitmap graphics file
- Educational treatment of GIF, PNG, and JPG file formats
- Dave Coffin's dcraw Converting digital camera raw image format files into other formats. Encapsulated PostScript, or EPS, is a DSC -conforming PostScript document with additional restrictions intended to make EPS files usable as a Graphics The File format SWF (acronym of " Shockwave Flash "pronounced swiff)a partially open repository for multimedia and especially Windows Metafile ( WMF) is a graphics file format on Microsoft Windows systems originally designed in the early 1990s This is a comparison of Image file formats. General Ownership of the format and related information
- Open Source Library supporting a large number of image formats
- Tips for file formats Determining which file formats to use.
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